The present invention relates to a mechanism for the drive of a tool spindle in a rotating indexing manner.
A mechanism for the drive of a tool spindle is the subject of U.S. Pat. No. 4,606,682. In the '682 patent, the tool spindle is connected, through a universal joint, to the connecting rod of a reciprocating drive constructed in the form of an eccentric drive. The tool spindle is surrounded by a guide sleeve, and a straight-line guide is provided between guide sleeve and tool spindle. A worm wheel is disposed on the guide sleeve and a helical guide is provided between the worm wheel and the guide sleeve. The worm wheel is in engagement with a worm which is driven by a motor as a result of which the tool spindle performs an indexing movement. The guide sleeve is in turn articulated on the connecting rod of a further eccentric drive which is connected to the reciprocating drive through a drive chain.
If the tool spindle performs reciprocating axial movements which the guide sleeve held fast, the tool of the tool spindle performs purely linear movements. On the other hand, if the guide sleeve is put into reciprocating axial movement by the further eccentric drive, then, as a result of the helical guide, the tool spindle additionally performs a rotary movement which leads to a helical movement of the tool. Since the two eccentric drives are adjustable with regard to their eccentricity, it is possible to vary the pitch of the helical movement continuously.
A disadvantage of the '682 patent is that it is extremely difficult to adapt the two eccentricities of the eccentric drives to one another so that the desired pitch of the helical movement results precisely.
In a further tool-spindle drive disclosed in DE-OS 33 14 524, a worm wheel is mounted on the tool spindle through a straight-line guide. The worm wheel is again in engagement with a worm, the shaft of which is axially displaceable. The axial displacement of a worm shaft is caused by means of a hydraulic motor which is controlled depending on the reciprocating drive for the tool spindle. If the tool spindle performs a reciprocating axial movement, the worm shaft is simultaneously moved backwards and forwards axially so that the tool spindle performs a helical movement The pitch of the helical movement can be varied depending on the direction and amplitude of the reciprocating axial movement of the worm shaft.
A disadvantage of the '524 patent is that it is practically impossible to synchronize the two axial movements with one another with the necessary accuracy in order to obtain the desired pitch of the helical movement.
A further tool-spindle drive mechanism is the subject of U.S. Pat. No. 4,695,209. The mechanism comprises a guide sleeve which is connected on the one hand to a tool spindle and on the other hand to a worm wheel for rotation therewith through, in each case, a helical guide. The two helical guides have the same pitch but in opposite directions. A first rocking lever is in engagement with the tool spindle and extends substantially at right-angles thereto, which rocking lever is articulately connected to an articulated lever which extends substantially parallel to the tool spindle. Articulated on this articulated lever is a second rocking lever which extends parallel to the first rocking lever and is in engagement with the guide sleeve. The one rocking lever has a pivot point fixed to the frame, which pivot point is displaceable along this rocking lever. The pivot point of the other rocking lever, which is fixed to the frame, is not adjustable. If the position of the displaceable pivot point is altered, the leverage is altered in the one rocking lever. The foregoing results in a variation in the pitch of the helical movement of the tool spindle which is not proportional to the variation in the position of the pivot point. A further disadvantage is that the ends of the rocking levers move over circular paths and so the lines of action of the transmission forces vary continuously, which is unfavorable for the whole stability, the bearing loading and hence for the tooth accuracy which can be achieved.
It would be highly desirable to improve the mechanism of the kinds mentioned above so as to achieve a linear adjustment of the pitch of the helical movement.
The foregoing object is achieved by way of the present invention by the provision of a two-part sliding loop with a sliding swivel joint between the two members, the rocking lever, as one member, only transmits linear movements to the other member and this sliding swivel joint can be displaced and located along the two members so that the pitch of the helical movement can be altered. Thus, a simple and very accurate manner of adjustment of the pitch of the helix of the workpiece to be produced results with a simultaneous simpler and more robust construction of the drive, which also renders possible a high stroke frequency. The pivot point of the rocking lever which is fixed to the frame is not adjustable in its position.